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Abstract:

An emission control catalyst is doped with bismuth, manganese, or bismuth
and manganese. The doped catalyst may be a palladium-gold catalyst or a
platinum-based catalyst, or both. The doped palladium-gold catalyst and
the doped platinum-based catalyst may be contained in a single washcoat
layer or in different washcoat layers of a multi-brick, multi-zoned, or
multi-layered emission control system. In all embodiments, zeolite may be
added as a hydrocarbon absorbing component.

Claims:

1. An engine exhaust catalyst comprising a palladium-gold catalyst doped
with bismuth or manganese, or bismuth and manganese.

2. The engine exhaust catalyst according to claim 1, further comprising a
platinum-based catalyst.

3. The engine exhaust catalyst according to claim 2, wherein the
platinum-based catalyst is doped with bismuth or manganese, or bismuth
and manganese.

5. An engine exhaust catalyst comprising multiple washcoat zones or
layers and a palladium-gold catalyst doped with bismuth or manganese, or
bismuth and manganese, is included in one of the washcoat zones or
layers.

6. The engine exhaust catalyst according to claim 5, wherein a
platinum-based catalyst is included in another one of the washcoat zones
or layers.

7. The engine exhaust catalyst according to claim 6, wherein the
platinum-based catalyst is doped with bismuth or manganese, or bismuth
and manganese.

13. An engine exhaust catalyst comprising multiple washcoat zones or
layers and a platinum-based catalyst doped with bismuth or manganese, or
bismuth and manganese, is included in one of the washcoat zones or
layers.

14. The engine exhaust catalyst according to claim 13, wherein a
palladium-based catalyst is included in another one of the washcoat zones
or layers.

15. The engine exhaust catalyst according to claim 14, wherein the
palladium-based catalyst is doped with bismuth or manganese, or bismuth
and manganese.

Description:

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] Embodiments of the present invention are directed to engine exhaust
catalysts and more particularly to engine exhaust catalysts doped with
bismuth or manganese.

[0003] 2. Description of the Related Art

[0004] Supported catalysts are quite useful in removing pollutants from
vehicle exhausts. Vehicle exhausts contain harmful pollutants, such as
carbon monoxide (CO), unburned hydrocarbons (HC), and nitrogen oxides
(NOx), that contribute to the "smog-effect" that have plagued major
metropolitan areas across the globe. Catalytic converters containing
supported catalysts and particulate filters have been used to remove such
harmful pollutants from the vehicle exhaust. While pollution from vehicle
exhaust has decreased over the years from the use of catalytic converters
and particulate filters, research into improved supported catalysts has
been continuing as requirements for vehicle emission control have become
more stringent and as vehicle manufacturers seek to use less amounts of
precious metal in the supported catalysts to reduce the total cost of
emission control.

[0005] The prior art teaches the use of supported catalysts containing
palladium and gold as good partial oxidation catalysts. As such, they
have been used extensively in the production of vinyl acetate in the
vapor phase by reaction of ethylene, acetic acid and oxygen. See, e.g.,
U.S. Pat. No. 6,022,823. As for vehicle emission control applications,
U.S. Pat. No. 6,763,309 speculates that palladium-gold might be a good
bimetallic candidate for increasing the rate of NO decomposition. The
disclosure, however, is based on a mathematical model and is not
supported by experimental data. There is also no teaching in this patent
that a palladium-gold system will be effective in treating vehicle
emissions that include CO and HC.

SUMMARY OF THE INVENTION

[0006] Embodiments of the present invention provide an emission control
catalyst doped with bismuth, manganese, or bismuth and manganese. The
doped catalyst may be a palladium-gold catalyst or a platinum-based
catalyst, or both. The doped palladium-gold catalyst and the doped
platinum-based catalyst may be contained in a single washcoat layer or in
different washcoat layers of a multi-brick, multi-zoned, or multi-layered
emission control system. In all embodiments, zeolite may be added as a
hydrocarbon absorbing component.

[0007] In a first embodiment, an engine exhaust catalyst includes a
palladium-gold catalyst doped with bismuth, manganese, or combinations
thereof. The engine catalyst may optionally include a platinum-based
catalyst. The platinum-based catalyst is optionally doped with bismuth,
manganese, or combinations thereof. For example, the platinum-based
catalyst is a platinum-palladium catalyst.

[0008] In a second embodiment, an engine exhaust catalyst includes
multiple washcoat zones or layers and a palladium-based catalyst doped
with bismuth or manganese, or bismuth and manganese, is included in at
least one of the washcoat zones or layers. In one example, the
palladium-based catalyst is palladium gold. The engine exhaust catalyst
may optionally include a platinum-based catalyst in the same or different
washcoat zones or layers. The platinum-based catalyst may be doped with
bismuth or manganese, or bismuth and manganese. In one example, the
platinum-based catalyst comprises a platinum-palladium catalyst.

[0009] In a third embodiment, an engine exhaust catalyst includes a
platinum-palladium catalyst doped with bismuth, manganese, or
combinations thereof. The engine catalyst may optionally include a
palladium-based catalyst. The palladium-based catalyst is optionally
doped with bismuth, manganese, or combinations thereof. For example, the
palladium-based catalyst is a palladium-gold catalyst.

[0010] In a fourth embodiment, an engine exhaust catalyst includes
multiple washcoat zones or layers and a platinum-based catalyst doped
with bismuth or manganese, or bismuth and manganese, is included in at
least one of the washcoat zones or layers. In one example, the
platinum-based catalyst is platinum-palladium. The engine exhaust
catalyst may optionally include a palladium-based catalyst in the same or
different washcoat zones or layers. The palladium-based catalyst may be
doped with bismuth or manganese, or bismuth and manganese. In one
example, the palladium-based catalyst comprises a palladium-gold
catalyst.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] So that the manner in which the above recited features of the
present invention can be understood in detail, a more particular
description of the invention, briefly summarized above, may be had by
reference to embodiments, some of which are illustrated in the appended
drawings. It is to be noted, however, that the appended drawings
illustrate only typical embodiments of this invention and are therefore
not to be considered limiting of its scope, for the invention may admit
to other equally effective embodiments.

[0012] FIGS. 1A-1D are schematic representations of different engine
exhaust systems in which embodiments of the present invention may be
used.

[0013]FIG. 2 is an illustration of a catalytic converter with a cut-away
section that shows a substrate onto which emission control catalysts
according to embodiments of the present invention are coated.

[0014] FIGS. 3A-3D illustrate different configurations of a substrate for
an emission control catalyst.

[0017]FIG. 6A shows the light-off data comparison for PdAuBi and PdAuMn
for CO oxidation in a first run. FIG. 6B shows the light-off data
comparison for PdAuBi and PdAuMn for CO oxidation a the second run.

[0018]FIG. 7A shows the light-off data comparison for PdAuMn for NO
conversion in a first run. FIG. 7B shows the light-off data comparison
for PdAuMn for NO conversion in a second run.

DETAILED DESCRIPTION

[0019] In the following, reference is made to embodiments of the
invention. However, it should be understood that the invention is not
limited to specific described embodiments. Instead, any combination of
the following features and elements, whether related to different
embodiments or not, is contemplated to implement and practice the
invention. Furthermore, in various embodiments the invention provides
numerous advantages over the prior art. However, although embodiments of
the invention may achieve advantages over other possible solutions and/or
over the prior art, whether or not a particular advantage is achieved by
a given embodiment is not limiting of the invention. Thus, the following
aspects, features, embodiments and advantages are merely illustrative and
are not considered elements or limitations of the appended claims except
where explicitly recited in the claims. Likewise, reference to "the
invention" shall not be construed as a generalization of any inventive
subject matter disclosed herein and shall not be considered to be an
element or limitation of the appended claims except where explicitly
recited in the claims.

[0020] FIGS. 1A-1D are schematic representations of different engine
exhaust systems in which embodiments of the present invention may be
used. The combustion process that occurs in an engine 102 produces
harmful pollutants, such as CO, various hydrocarbons, particulate matter,
and nitrogen oxides (NOx), in an exhaust stream that is discharged
through a tail pipe 108 of the exhaust system.

[0021] In the exhaust system of FIG. 1A, the exhaust stream from an engine
102 passes through a catalytic converter 104, before it is discharged
into the atmosphere (environment) through a tail pipe 108. The catalytic
converter 104 contains supported catalysts coated on a monolithic
substrate that treat the exhaust stream from the engine 102. The exhaust
stream is treated by way of various catalytic reactions that occur within
the catalytic converter 104. These reactions include the oxidation of CO
to form CO2, burning of hydrocarbons, and the conversion of NO to
NO2.

[0022] In the exhaust system of FIG. 1 B, the exhaust stream from the
engine 102 passes through a catalytic converter 104 and a particulate
filter 106, before it is discharged into the atmosphere through a tail
pipe 108. The catalytic converter 104 operates in the same manner as in
the exhaust system of FIG. 1A. The particulate filter 106 traps
particulate matter that is in the exhaust stream, e.g., soot, liquid
hydrocarbons, generally particulates in liquid form. In an optional
configuration, the particulate filter 106 includes a supported catalyst
coated thereon for the oxidation of NO and/or to aid in combustion of
particulate matter.

[0023] In the exhaust system of FIG. 1C, the exhaust stream from the
engine 102 passes through a catalytic converter 104, a pre-filter
catalyst 105 and a particulate filter 106, before it is discharged into
the atmosphere through a tail pipe 108. The catalytic converter 104
operates in the same manner as in the exhaust system of FIG. 1A. The
pre-filter catalyst 105 includes a monolithic substrate and supported
catalysts coated on the monolithic substrate for the oxidation of NO. The
particulate filter 106 traps particulate matter that is in the exhaust
stream, e.g., soot, liquid hydrocarbons, generally particulates in liquid
form.

[0024] In the exhaust system of FIG. 1D, the exhaust stream passes from
the engine 102 through a catalytic converter 104, a particulate filter
106, a selective catalytic reduction (SCR) unit 107 and an ammonia slip
catalyst 110, before it is discharged into the atmosphere through a tail
pipe 108. The catalytic converter 104 operates in the same manner as in
the exhaust system of FIG. 1A. The particulate filter 106 traps
particulate matter that is in the exhaust stream, e.g., soot, liquid
hydrocarbons, generally particulates in liquid form. In an optional
configuration, the particulate filter 106 includes a supported catalyst
coated thereon for the oxidation of NO and/or to aid in combustion of
particulate matter. The SCR unit 107 is provided to reduce the NOx
species to N2. The SCR unit 107 may be ammonia/urea based or hydrocarbon
based. The ammonia slip catalyst 110 is provided to reduce the amount of
ammonia emissions through the tail pipe 108. An alternative configuration
places the SCR unit 107 in front of the particulate filter 106.

[0025] Alternative configurations of the exhaust system includes the
provision of SCR unit 107 and the ammonia slip catalyst 110 in the
exhaust system of FIG. 1A or 1C, and the provision of just the SCR unit
107, without the ammonia slip catalyst 110, in the exhaust system of
FIGS. 1A, 1B or 1C.

[0026] As particulates get trapped in the particulate filter within the
exhaust system of FIG. 1B, 1C or 1D, it becomes less effective and
regeneration of the particulate filter becomes necessary. The
regeneration of the particulate filter can be either passive or active.
Passive regeneration occurs automatically in the presence of NO2.
Thus, as the exhaust stream containing NO2 passes through the
particulate filter, passive regeneration occurs. During regeneration, the
particulates get oxidized and NO2 gets converted back to NO. In
general, higher amounts of NO2 improve the regeneration performance,
and thus this process is commonly referred to as NO2 assisted
oxidation. However, too much NO2 is not desirable because excess
NO2 is released into the atmosphere and NO2 is considered to be
a more harmful pollutant than NO. The NO2 used for regeneration can
be formed in the engine during combustion, from NO oxidation in the
catalytic converter 104, from NO oxidation in the pre-filter catalyst
105, and/or from NO oxidation in a catalyzed version of the particulate
filter 106.

[0027] Active regeneration is carried out by heating up the particulate
filter 106 and oxidizing the particulates. At higher temperatures,
NO2 assistance of the particulate oxidation becomes less important.
The heating of the particulate filter 106 may be carried out in various
ways known in the art. One way is to employ a fuel burner which heats the
particulate filter 106 to particulate combustion temperatures. Another
way is to increase the temperature of the exhaust stream by modifying the
engine output when the particulate filter load reaches a pre-determined
level.

[0028] The present invention provides catalysts that are to be used in the
catalytic converter 104 shown in FIGS. 1A-1D, or generally as catalysts
in any vehicle emission control system, including as a diesel oxidation
catalyst, a diesel filter catalyst, an ammonia-slip catalyst, an SCR
catalyst, or as a component of a three-way catalyst. The present
invention further provides a vehicle emission control system, such as the
ones shown in FIGS. 1A-1D, comprising an emission control catalyst
comprising a monolith and a supported catalyst coated on the monolith.

[0029]FIG. 2 is an illustration of a catalytic converter with a cut-away
section that shows a substrate 210 onto which supported metal catalysts
are coated. The exploded view of the substrate 210 shows that the
substrate 210 has a honeycomb structure comprising a plurality of
channels into which washcoats containing supported metal catalysts are
flowed in slurry form so as to form coating 220 on the substrate 210.

[0030] FIGS. 3A-3D illustrate different embodiments of the present
invention. In the embodiment of FIG. 3A, coating 220 comprises two
washcoat layers 221, 223 on top of substrate 210. Washcoat layer 221 is
the bottom layer that is disposed directly on top of the substrate 210.
Washcoat layer 223 is the top layer that is in direct contact with the
exhaust stream. Based on their positions relative to the exhaust stream,
washcoat layer 223 encounters the exhaust stream before washcoat layer
221.

[0031] In the embodiment of FIG. 3B, coating 220 comprises three washcoat
layers 221, 222, 223 on top of substrate 210. Washcoat layer 221 is the
bottom layer that is disposed directly on top of the substrate 210.
Washcoat layer 223 is the top layer that is in direct contact with the
exhaust stream. Washcoat layer 222 is the middle layer that is disposed
in between washcoat layers 221, 223. The middle layer is also referred to
as a buffer layer. Based on their positions relative to the exhaust
stream, washcoat layer 223 encounters the exhaust stream before washcoat
layers 221, 222, and washcoat layer 222 encounters the exhaust stream
before washcoat layer 221.

[0032] In the embodiment of FIG. 3c, the substrate 210 is a single
monolith that has two coating zones 210A, 210B. A first washcoat is
coated onto a first zone 210A and a second washcoat is coated onto a
second zone 210B. In the embodiment of FIG. 3D, the substrate 210
includes first and second monoliths 231, 232, which are physically
separate monoliths. A first washcoat is coated onto the first monolith
231 and a second washcoat is coated onto the second monolith 232.

[0033] All of the embodiments of the present invention include an engine
exhaust catalyst doped with bismuth (Bi) or manganese (Mn), or both. The
engine exhaust catalyst includes a supported platinum-palladium catalyst
or a supported palladium-gold catalyst, or both. Bi doping shows
enhancement on CO conversions for both Pt-Pd catalyst and Pd-Au catalyst.
Mn doping shows enhancement on both CO and NO conversions for both Pt-Pd
catalyst and Pd-Au catalyst.

[0048] Drop wise add solution made in step 2 to the 1.96 g of powder
prepared in step 1 while stirring. Keep at room temperature for 1 hr.

[0049] Dry at 120° C. for 4 hrs.

Light-Off Test Conditions

[0050] All the tests are in the condition of 1000 ppm CO; 105 ppm
C3H8, 245 ppm C3H6, 450 ppm NOx. During the run,
gas mixtures were flowed at 35° C. for 15 min, 35° C. to
300° C. (10° C./min) in 1st run, cool down in full gas
mixture to 50° C., then ramp to 300° C. (10° C./min)
in 2nd run. Samples used were 10 mg samples diluted with 90 mg
α-alumina.

[0051]FIG. 4 shows the light-off data comparison for PtPdBi and PtPdMn
for CO oxidation. All the catalysts were calcined at 500° C. for 2
hrs. before testing.

[0052]FIG. 5 shows the light-off data comparison for PtPdBi and PtPdMn
for C3H6 conversion. All the catalysts were calcined at
500° C. for 2 hrs. before testing.

[0053]FIG. 6A shows the light-off data comparison for PdAuBi and PdAuMn
for CO oxidation in the first run. FIG. 6B shows the light-off data
comparison for PdAuBi and PdAuMn for CO oxidation in the second run. All
the catalysts were calcined at 500° C. for 2 hrs. before testing.

[0054]FIG. 7A shows the light-off data comparison for PdAuMn for NO
conversion in the first run. FIG. 7B shows the light-off data comparison
for PdAuMn for NO conversion in the second run. All the catalysts were
calcined at 500° C. for 2 hrs. before testing.

[0055] A first embodiment of the present invention is an engine exhaust
catalyst having a single washcoat layer design containing either
palladium-gold or platinum-palladium, or both, doped with bismuth,
manganese, or both. The doped catalysts are better than either undoped
versions at least in CO light off. In the monolith reactor, laminar flow
in the channel helps utilize exotherm generated by early CO oxidation for
HC oxidation. If palladium gold is included, the weight ratio of the
palladium to gold may be from 3:1 to 1:3, preferably, from 2:1 to 1:2. If
platinum palladium is included, the weight ratio of the platinum to
palladium may be from 4:1 to 1:4, preferably, from 3:1 to 1:2. The
catalyst may be doped with bismuth in an amount from about 0.2% to 5% by
weight of the catalyst, preferably, from 1% to 3% by weight of the
catalyst. Alternatively, the catalyst may be doped with manganese in an
amount from about 0.2% to 5% by weight of the catalyst, preferably, from
1% to 3% by weight of the catalyst. Bismuth and manganese both may be
included in an amount from about 0.2% to 10% by weight of the catalyst,
preferably, from 2% to 6% by weight of the catalyst.

[0056] A second embodiment of the present invention is an engine exhaust
catalyst having 2-layer design or a 3-layer design, where each of the
layers may include platinum-palladium, palladium-gold, or both. For
example, in a two layer design, one of the layers contains
platinum-palladium and the other layer contains palladium-gold. For the
palladium gold catalyst, the weight ratio of the palladium to gold may be
from 3:1 to 1:3, preferably, from 2:1 to 1:2. For the platinum palladium
catalyst, the weight ratio of the platinum to palladium may be from 4:1
to 1:4, preferably, from 3:1 to 1:2. Bismuth, manganese, or both can be
applied in any of the layers and to platinum-palladium, palladium-gold,
or both. The catalyst may be doped with bismuth in an amount from about
0.2% to 5% by weight of the catalyst, preferably, from 1% to 3% by weight
of the catalyst. Alternatively, the catalyst may be doped with Manganese
in an amount from about 0.2% to 5% by weight of the catalyst, preferably,
from 1% to 3% by weight of the catalyst. Bismuth and manganese both may
be included in an amount from about 0.2% to 10% by weight of the
catalyst, preferably, from 2% to 6% by weight of the catalyst. In another
embodiment, one of the layers may include platinum catalyst or palladium
catalyst.

[0057] Embodiments of the present invention include providing the doped
catalyst in one or more zones of the substrate. Therefore, the
description herein with respect to washcoat layers applies equally to
providing metal particles in zones containing platinum-palladium,
palladium-gold, or both, doped with bismuth, manganese, or both. In one
embodiment, instead of the coating the monolith with the supported
catalysts in washcoat layers, the catalysts may be coated on the monolith
using two or more coating zones, as shown in FIGS. 3C and 3D. For
example, instead of three layers, the monolith may be coated with three
zones of catalysts. In yet another embodiment, the monolith may be coated
with a combination of zones and layers of different catalyst
formulations. If desired, the zones and/or layers may overlap to provide
even more flexibility for the catalyst design.

[0058] In the embodiments described herein, the engine exhaust catalyst
may optionally include one or more zeolites such as ZSM5 zeolite, HY
zeolite, beta zeolite, mordenite, ferrierite, and combinations thereof.
In some embodiments, ceria (CeO2) and alumina (Al2O3) may
be added as components. The zeolites and other components may be included
in one or more of the washcoat layers.

[0059] In summary, Bi and Mn doped PtPd and PdAu are better than non-doped
in CO oxidation. Bi doping may be less efficient for hydrocarbon
oxidation, but reaction heat generated by early CO light off should be
helpful for hydrocarbon light off in monolith reactor. Mn doping enhances
NO oxidation activity as well. It is promising if making NO2 is
desired. Incorporating Bi and Mn in engine exhaust catalysts containing
palladium-gold should result in cost reduction.

[0060] In one embodiment, an engine exhaust catalyst includes a
palladium-gold catalyst doped with bismuth, manganese, or combinations
thereof. In another embodiment, the engine catalyst may also include a
platinum-based catalyst. The platinum-based catalyst is optionally doped
with bismuth, manganese, or combinations thereof. For example, the
platinum-based catalyst is a platinum-palladium catalyst.

[0061] In another embodiment, an engine exhaust catalyst includes multiple
washcoat zones or layers and a palladium-based catalyst doped with
bismuth or manganese, or bismuth and manganese, is included in one of the
washcoat zones or layers. In one embodiment, the palladium-based catalyst
is palladium gold. The engine exhaust catalyst may optionally include a
platinum-based catalyst in another one of the washcoat zones or layers.
The platinum-based catalyst may be doped with bismuth or manganese, or
bismuth and manganese. In one example, the platinum-based catalyst
comprises a platinum-palladium catalyst.

[0062] While particular embodiments according to the invention have been
illustrated and described above, those skilled in the art understand that
the invention can take a variety of forms and embodiments within the
scope of the appended claims.